Flattening a sheet metal panel?

[Morrisman]

So, I'm working on the bed for the V8 trike and had to add some 1 mm steel where I'd cut too much off. As it's been mig seam welded it's bellied in, or out, oil canned, or whatever the term is. I clamped it flat to a 1/4" steel plate as I welded but predictably that didn't work.

How would one go about getting this flat? There is a 10mm round bar to be welded around the edge, but it's still wobbling all over the place. I'm thinking the welds probably need peening, with something heavy and solid behind, to stretch the welded area a bit.

Its not really that important, as it will be behind the wheels and mudguards, but it would be nice to know the technique to put it right.

 

[500e]

Don't think I have done it on 1mm but the technique is to heat to red hot a spot the size of a 2 P price have a helper to hold the torch, body weight behind tap around the red spot lastly knock the centre flat.
The hard part is knowing where to put the shrinking spots you may need more than one.
I learnt on EA vans very satisfying to get a big flat panel. tight
Work the panel by hand and try to feel/see where it is stretched

 

[DAPPH]

Look up using a bastard file shaped as a riffler to shrink bubble patches in red hot panels with a flatter behind it . Use a very small acetylene torch & small flame so you only heat the immediate area's .

 

[500e]

If you use a bastard grind most of its teeth off as @DAPPH said
Small flame is good + quick heat & cool the panel with a wet rag after each spot, it's surprising how much residual heat moves the panel
Oxy acetaline needed realy

 

[DAPPH]

Grind the teeth off the bastard

You need some teeth to pucker the bubble before flattening it

 

[500e]

Never used a file/slapper used a panel hammer beat round spot then last blow flattens the red hot spot shrinking it..
Just different techniques I expect and different teachers

 

[Agroshield]

If you want to see it in action, start at 7:45

 

[Burdekin]

Mig is harder to do but plannish the weld, hammer and dolly to stretch the weld. You only want to do it on the weld and if you’re lucky it should go back to how it was before you welded it. Tig or oxy would be no issue as they are softer but mig is hard, especially if you cooled it fast when welding but give it a go. Don’t shrink it as recommended above, your issue is the weld has shrunk and pulled the metal in at the weld, shrinking more will make it worse. The stress is in the weld area and is the only area you need to worry about. Give it a wee grind flat first as well.

 

[500e]

Always prep the panel eg. Finish all welding, grind welds back, as @Burdoni said.
MIG is a harder as you noticed when flatting the weld, you still have look for the root of the. oil canning it can produce the problem off the weld aeria

 

[Morrisman]

If you want to see it in action, start at 7:45

That's an interesting vid. I know a bit about heat shrinking etc, it's quite useful.

As Burdekin points out, my sheet has shrunk in the middle, where welded, so heating red dots around it probably won't work. I'll have a go at pounding on the welds with a dolly behind.

 

[Burdekin]

I did a thread on oxy welding a flat sheet but pics are gone, this is a good video to show the technique. Works well with oxy and Tig and to a lesser extent mig.

and another shows the technique and talks about what happens when you weld and how it shrinks at the weld.

 

[Morrisman]

I did a thread on oxy welding a flat sheet but pics are gone, this is a good video to show the technique. Works well with oxy and Tig and to a lesser extent mig.

and another shows the technique and talks about what happens when you weld and how it shrinks at the weld.

It's amazing what some of those body guys can do, then run bare steel bodies so the amazing metalwork can be seen.

 

[Morrisman]

I did a bit of beating along the welds, hammer and dolly, and it made a fair bit of difference. Its nowhere near perfect but definitely better. Should have taken some better pics, but it looks flat, to the eye.

 

[Myles1970]

If you want to see it in action, start at 7:45

Great visual explanation!